Mobile control methods for internet protocol (IP) communication in mobile communication, such as mobile phones, are currently being examined. In local mobility over a limited area in which a single network manager performs a service, a method is being examined for performing network control without a terminal changing an IP address when the terminal moves (for example, Internet Engineering Task Force [IETF] netlmm group). Regarding a demand such as this, a device on a network side is required to support movement processing of the terminal and perform control such that an IP packet is transferred to an appropriate base station to which the mobile terminal is connected. According to a draft stating specific requirement conditions, in an access network such as this, improvement in usage efficiency in wired segments of the network and similar improvement in usage efficiency in wireless segments of the network are required to improve performance of a handover. At the same time, movement control is also required to be performed without the IP address of the terminal being changed. Moreover, a requirement condition is given that changes cannot be made to an IP stack of the terminal to actualize the requirements described above.
In Mobile IP that is a representative movement control, a packet is transferred to a correct location by a tunnel technology that uses an IP address (referred to, hereinafter, as a home address [HoA]) indicating an address of a host and an IP address (referred to, hereinafter, as a care-of-address [CoA]) indicating a location. However, in mobile IP (MIP), processes are performed by the terminal, such as the terminal itself creating a new address (CoA) and registering a mapping of the address to a home agent (HA). These processes cause decrease in handover performance. Because the tunnel ends at the terminal, the tunnel is used even in a wireless segment, causing a problem with overhead of a tunnel header in data. In MIP, to improve handover performance, an HMIP is also being examined that introduces a mobile anchor point (MAP) that manages position registration in a limited area. In this case, within a certain limited area, only position registration is required to be performed to the MAP. Therefore, signaling distance and time are shortened. However, duplicate tunnel headers are required, and network resources decrease. In addition, because the terminal is required to newly perform signaling to the MAP, a change is required to be made to the IP stack of the terminal. Therefore, in an access network in which a single network manager performs a service, as described above, various proposals are being made to efficiently perform local mobility without changes being made to the terminal.
FIG. 6 is a configuration of an access network described in Non-patent Document 1 below. A localized mobility management domain (LMMD)#1 that is an access network is a network in which a border gateway (BG) and access routers (AR#1, AR#2, and AR#3) are connected. The BG serves as a connection point with an external network to which a correspondent node (CN) is connected. The AR#1, the AR#2, and the AR#3 function as wireless base stations connecting with a mobile terminal (mobile node [MN]) and serve as relay devices. In the example, to simplify explanation, the access router and the wireless base station (BS or AP) are provided as functions of a same device. An area of a network such as this is referred to, hereinafter, as a “Netlmm” domain.
In the Netlmm domain, the AR#1, the AR#2, and the AR#3 each have a different prefix (prefix#1, prefix#2, and prefix#3). Moreover, each AR#1, AR#2, and AR#3 has a table allowing the AR#1, the AR#2, and the AR#3 to respectively acquire IP addresses of the AR#1, the AR#2, and the AR#3 having the “prefix#1”, the “prefix#2”, and the “prefix#3” by using the “prefix#1”, the “prefix#2”, and the “prefix#3”.
In FIG. 6,
1. when an MN#1 is started, the MN#1 acquires the “prefix#1” from the AR#1 to which the MN#1 is connected and creates an IP address of the MN#1 itself (IP-MN#1). The AR#1 at this time is referred to as a home access router (HAR). Because the MN#1 communicates using the IP address (IP-MN#1) created from the “prefix#1” that can be routed, when the MN#1 is connected under the control of the HAR, the MN#1 can perform communication by a normal IP routing without using a tunnel when communicating with the CN.
When the MN#1 moves to be under the control of another AR, a following process is performed.
2. When the MN#1 transmits a router solicitation message (referred to, hereinafter, as RS) after acknowledging disconnection from the AR#1 before movement, and the MN#1 receives a router advertisement message (referred to, hereinafter, as RA) from a new AR, or when the MN#1 receives a periodic RA from a new AR and the like and receives a different “prefix”, the MN#1 recognizes that the MN#1 itself has moved to be under the control of another AR (AR#2, herein). At this time, the MN#1 uses a Global IP address that the MN#1 itself is using and transmits a message (Activate message) indicating that the MN#1 wishes to perform communication.
3. The AR#2 that receives the Activate message recognizes the “prefix#1” from the Global IP address being used and transmits a position update message (Location Update) to the AR#1 having the “prefix#1”. An AR#2 such as this is referred to as a visited access router (VAR).
4. The HAR (=AR#1) that receives the Location Update acknowledges that the MN#1 that had been under the control of the HAR itself has moved to be under the control of the VAR (=AR#2). The HAR (=AR#1) establishes a tunnel between the HAR (=AR#1) and the VAR (=AR#2). After receiving a packet destined to the MN#1, the HAR (=AR#1) uses the tunnel and transfers the packet to the VAR (=AR#2). As a result, the VAR (=AR#2) can transmit the received packet destined to the MN#1 to the MN#1 connected to be under the control of the VAR (=AR#2) itself. Through use of the tunnel between the HAR and the VAR such as this, the MN can continue communication always using a same IP address within the “Netlmm” domain.
FIG. 7 shows an overview of a communication performed using the tunnel during movement of the MN. As shown in FIG. 7(a), when the MN is turned ON (Power On), the MN acquires a “prefix1” from an AR1 to which the MN is connected and creates an address IP1. Then, as shown in FIG. 7(b), when the MN connects to an AR2 as a result of movement (Start Communication), the MN transmits an “Activate Message” using the IP1. As a result, the AR2 operates as the VAR of the MN, and a tunnel is established between the AR1 and the AR2. Here, even when the MN starts communication with the CN while under the control of the AR2, the MN performs the communication using the tunnel between the AR1 and the AR2. Moreover, as shown in FIG. 7(c), when the MN moves to be under the control of an AR3 (Continue Communication), the AR3 becomes the VAR of the MN. Transfer of the packet addressed to the IP1 can be performed as a result of the tunnel being changed to be between the AR1 and AR3. In this way, when the MN moves within the “Netlmm” domain, the MN can continue communication without changing the IP address.
As another conventional example, neighbor discovery is described in Non-patent Document 2, below.    Non-Patent Document 1: draft-diaretta-netlmm-protocol-00-txt, FIG. 1—Reference architecture, Oct. 14, 2005    Non-Patent Document 2: RFC2461
However, although “Netlmm” requires that a configuration of the MN is not changed, when a method such as this is used, the MN is required to give notification of an IP address that the MN wishes to use as the “Activate Message”, when the MN moves. The configuration of the MN is required to be changed.
When, in adherence to the requirement conditions of “Netlmm”, a normal MN of which the configuration is not changed is used, an operation such as the following can be considered. Ordinarily, when the MN receives a new “Prefix”, the MN creates a new IP address when an A bit within a “Prefix Option” of the “Prefix” is set, and performs a duplicate address detection (DAD). In this case, an AR that receives a Neighbor Solicitation message (referred to, hereinafter, as NS) for checking the DAD of the new address cannot recognize the movement of the MN and is considered to operate as the HAR of the MN at the relevant address. However, in this case, if the MN is an MN including a MIP because the MN has moved to a different network, the CoA is changed and a Binding Update message (referred to, hereinafter, as BU) is transmitted to the HA.
When it is thought that a Detecting Network Attachment (DNA) that detects network movement, shown in Non-patent Document 2, is used, the MN does not perform acknowledgement that the MN has moved to a different network. However, the MN still creates the new IP address and performs DAD. In this case as well, the MN creates an IP address every time the MN moves, causing the MN to hold a plurality of IP addresses. In an instance such as this, the MN may communicate or may be communicating using the address before movement. In an instance such as this, a tunnel is required to be established between the MN and the AR holding the relevant “Prefix”, and a transfer of the packet is required to be performed correctly. However, ordinarily, the AR of a movement destination cannot know which AR is the HAR of the address used by the MN to perform communication until the AR of the movement destination receives the packet from the MN using the “Prefix” before movement. Therefore, the tunnel is not established until data from the MN is received. A packet loss occurs. Moreover, because the network cannot control which IP address the MN uses, a problem occurs in that a signaling amount for control, such as a large number of tunnels being established for the plurality of IP addresses used by the MN and the tunnels being reconfigured every time the MN moves, increases.
Hereafter, an operation is described of when a normal MN is used to meet the requirement conditions of “Netlmm”. FIG. 8 shows an overview of communication performed during movement. FIG. 9 shows a sequence during the movement. In FIG. 8, AR1 to AR5 are present. MN starts at the AR1 and moves in a direction towards the AR 5. The MN creates an address using a “Prefix” received from the AR1 to AR5 every time the MN moves, and communicates using the created addresses. FIG. 8(a) shows a state in which the MN is performing communication under the control of the AR3. At this time, it is assumed that the MN has started communication using the respective addresses of the AR1, the AR2, and the AR 3, while being connected to the AR2, and the AR 3. Therefore, the HAR of the addresses IP1, IP2, and IP3 are respectively AR1, AR2, and AR3. Respective communication with the AR1, the AR2, and the AR 3 are performed by a tunnel being established between the AR1, the AR2, and the AR 3 and the AR3 that becomes the VAR.
FIG. 8(b) shows a state in which the MN moves to the AR5. When the three communication operations are continued, every time the AR5 receives data from the MN, the AR5 acknowledges the AR serving as the HAR from the “Prefix” and reconfigures the tunnel. When communication using an address IP4 has not been performed, the tunnel to the AR4 is not established. In this way, because the created addresses increase every time the MN moves, a load of reconfiguring the tunnel during movement increases as the IP addresses used increases in the MN.
FIG. 9 shows a sequence during movement. In the diagram, a flow of a process performed when the MN that has been communicating under the control of the AR2 moves to be under the control of the AR3. For example, the MN had been connected to the AR1 before being connected to the AR2 and has been communicating using the address IP1 of when the MN was connected to the AR1. When a layer 2 handover (L2 HO from AR2 to AR3) from the AR2 to the AR3 is completed, connection to the AR2 that had been a default router (DR) until this point is broken. Therefore, to check the connection with the AR2, the MN transmits a NS addressed to the AR2. Because the AR2 responding to the NS no longer has a connection relationship with the MN, the MN does not receive a response packet. The MN acknowledges that the connection with the DR(=AR2) has been broken as a result of three NS failures (Detect unreachability to AR2).
Subsequently, the MN transmits a RS to acquire router information of a new link and confirms that the MN is newly in a “Prefix 3” link by an RA responded by the AR3. At this time, that there are no changes in “IP link” can be recognized through use of a same “Landmark Option” by DNA. The MN creates an address IP3 from the received “Prefix 3” (Create new IP address). A state of the IP address of the MN at this time is held at “Preferred” for all IP1, IP2, and IP3, between “Preferred state/Deprecated state”. Therefore, the MN can use any address for a new communication.
After creating the address IP3, the MN checks for duplicate addresses through DAD. As a result, the AR3 acknowledges that the AR3 itself is the HAR of the IP3. Then, the AR3 acknowledges that an IP address (IP1) using a different “Prefix” is present at a timing at which a data packet that the MN is communicating is outputted. As a result, the AR3 acquires a relevant other HAR (=AR1) of the MN from the table set in advance and performs a “Location Update” of the IP1 to the HAR (=AR1). As a result, regarding the IP1, a new tunnel to the AR3 to which the MN has newly moved is established, allowing communication to be restarted.
However, at this time, when communication is performed using an application in which few packets are transmitted by the MN (for example, a user datagram protocol [UDP] in which the MN mainly receives data), the AR3 cannot know that the MN is using that address for communication until the MN outputs data (Data [IP-1]). Therefore, as shown in FIG. 9, a packet addressed to the IP2 received by the AR2 as before is destroyed because a transfer destination is unknown. The MN acknowledges that communication between the AR3 and the AR2 is required for the first time when the MN transmits a packet having the IP2 as a source address and establishes a tunnel. In this way, when a normal MN to which no changes have been made is used, in addition to signaling for performing movement management of a plurality of tunnels increasing, packet loss increases because reconfiguration of the tunnel cannot be performed immediately after movement.